Brennen McKenzie, MA, MSc, VMD

Dogs and humans are uniquely connected as species. Studies have found that 

dogs are even much better than chimpanzees

, our closest evolutionary relatives, at understanding human gestures and communication. For tens of thousands of years, dogs have lived symbiotically with humans, and for at least several hundred years we have intensively bred and shaped dogs to participate in human society. As hunting companions, protectors, and increasingly as members of our close family, dogs are bonded to us and integrated into our lives unlike any other animal.

One consequence of this relationship is that dogs are well-suited to help us understand and manage aging, a biological process with a multitude of factors, many of which are tied to lifestyle and habits. Unlike laboratory animal models, such as rats and mice, dogs share our environments, routines, and the same potential risk factors for death and disease. This makes dogs a more relevant model of natural aging than animals in controlled research settings.

Dogs also share many of the diseases and causes of death as humans. While they grow and age faster than us, they do so in similar ways. Injury and infections, for example, are more common in young dogs as they are in young people, whereas older humans and dogs are more likely to experience cancer or degenerative diseases. These similarities allow research data from dogs to be more readily applied to human health than data from lab animal species. The shorter lifespan of dogs also allows us to study aging and longevity therapies on a more practical timescale than similar studies with humans.

Comparing how dogs and humans age. From 1. Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. 

Another advantage of studying our faithful companions is the fact that intensive breeding in dogs has produced perhaps the greatest degree of variation within any species. This includes physical differences, such as the huge variation in size from the toy breeds such as the Yorkshire Terrier to giants like the Great Dane or Irish Wolfhound, and of course, variation in how dogs age. Large breeds age faster and live shorter lives than smaller breeds. Investigating these differences can give us unique insights into the underlying mechanisms of aging that are harder to identify in other species with less intraspecific variation.

There is also a comprehensive scientific healthcare system in place for dogs as well as humans, which allows not only medical testing and treatment for individual dogs but widespread research on aging and age-associated health problems. There is also ample demand and resources for this research because so many of us love dogs and are willing to contribute time, effort, and money to improving canine health. 

While there are, of course, important biological differences between humans and dogs, our canine companions are uniquely suited to help us understand our own aging. Helping us to understand and alter our own aging is just one more of the many gifts our canine best friends bring into our lives.

Dogs are great models for aging biology

Dogs and humans are uniquely connected as species. Studies have found that <a href="https://www.sciencedaily.com/releases/2012/02/120208180251.htm">dogs are even much better than chimpanzees</a>, our closest evolutionary relatives, at understanding human gestures and communication. For tens of thousands of years, dogs have lived symbiotically with humans, and for at least several hundred years we have intensively bred and shaped dogs to participate in human society. As hunting companions, protectors, and increasingly as members of our close family, dogs are bonded to us and integrated into our lives unlike any other animal.



One consequence of this relationship is that dogs are well-suited to help us understand and manage aging, a biological process with a multitude of factors, many of which are tied to lifestyle and habits. Unlike laboratory animal models, such as rats and mice, dogs share our environments, routines, and the same potential risk factors for death and disease. This makes dogs a more relevant model of natural aging than animals in controlled research settings.



Dogs also share many of the diseases and causes of death as humans. While they grow and age faster than us, they do so in similar ways. Injury and infections, for example, are more common in young dogs as they are in young people, whereas older humans and dogs are more likely to experience cancer or degenerative diseases. These similarities allow research data from dogs to be more readily applied to human health than data from lab animal species. The shorter lifespan of dogs also allows us to study aging and longevity therapies on a more practical timescale than similar studies with humans.



<figure class="wp-block-image"><img decoding="async" src="https://lh5.googleusercontent.com/Y2YiLEfNaIWJ6U3k2-sUHGwAAvCj1izu5LISlDgDe6C5Hg7sAdqdamBhJpL62vh1Ajzgpasm6OAa-70P6gTBzf7p9W5-UraJiN8brzB67zaYBDU_cO5E45k1NzEOJp5ZIDN9i2mr" alt=""/><figcaption>Comparing how dogs and humans age. From 1.&nbsp;Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome.&nbsp;Cell Syst. 2020;11(2):176-185.</figcaption></figure>



Another advantage of studying our faithful companions is the fact that intensive breeding in dogs has produced perhaps the greatest degree of variation within any species. This includes physical differences, such as the huge variation in size from the toy breeds such as the Yorkshire Terrier to giants like the Great Dane or Irish Wolfhound, and of course, variation in how dogs age. Large breeds age faster and live shorter lives than smaller breeds. Investigating these differences can give us unique insights into the underlying mechanisms of aging that are harder to identify in other species with less intraspecific variation.



There is also a comprehensive scientific healthcare system in place for dogs as well as humans, which allows not only medical testing and treatment for individual dogs but widespread research on aging and age-associated health problems. There is also ample demand and resources for this research because so many of us love dogs and are willing to contribute time, effort, and money to improving canine health.&nbsp;



While there are, of course, important biological differences between humans and dogs, our canine companions are uniquely suited to help us understand our own aging. Helping us to understand and alter our own aging is just one more of the many gifts our canine best friends bring into our lives.

From birth to physical maturity, there is a rapid increase in function and ability to cope with external stressors in all dogs. Then, as dogs age, health and function begin to decay until death eventually occurs, either directly from a disease or, more often, because humans are forced to make the difficult choice to euthanize a dog because of pain or poor quality of life.  Lifespan is simply the amount of time a dog is alive. Healthspan is the period of life where they are living full, healthy lives, before any major illness or functional decline.

The figure below shows different possible trajectories for a dog’s life. Increasing healthspan means giving dogs more time in good health. A treatment that extends healthspan can slow age-related decline in health and increase this proportion of life spent in good health 

The impact of increasing healthspan on minimizing the period of poor health preceding death. From McKenzie, BA. Lacroix-Fralish, ML. Chen, F. (2022)The phenotype of aging in the dog: A narrative review. J Amer Vet Med Assoc.

In our view, the goal of maximizing healthspan is equally, if not more important than extending lifespan. Therapies which delay death but do not prolong healthspan might actually reduce overall quality of life by prolonging the period of disability preceding death. Giving dogs and their humans more good quality time together means extending the period of good health, not just the length of life. 

Of course, any therapy which extends healthspan will automatically extend lifespan for many dogs because the number one cause of death is euthanasia. If we improve quality of life and function in older dogs, owners will be able to have more joyful time with their canine companions. 

Currently, veterinary medicine tends to focus on diagnosing, treating, and sometimes preventing individual disease. However, the most important underlying cause for nearly all diseases in adult dogs is aging. The most effective way to extend the healthy period of life is to target the basic mechanisms of aging that reduce our function and ability to cope with stress and/or fight off disease. Targeting these mechanisms could potentially prevent 

 heart disease and cancer in many dogs, as well as many other diseases we tend to think of as unrelated. 

Healthspan isn’t easy to measure. What is considered “good health” is subjective. The goal of preventing all age-related changes in function and all disease probably isn’t realistic, at least for now. A more practical approach is to consider the number of age-related illnesses that occur, the age at which they happen, and the overall quality of life dogs experience. If we can find treatments that have a clear impact on these measures, we can say we are extending healthspan, and we are likely to also be extending lifespan by improving quality of life and delaying death from illness and euthanasia. As our understanding of aging in dogs improves, and as we develop better tools to measure health and quality of life, we will continue to make progress towards our goals of extending healthspan and giving dogs and their humans more good time together.

Loyal recruited over 500 dogs to participate in a study assessing two tools for measuring frailty and health-related quality of life in dogs.

Healthspan: the healthy prime of life

<p id="from-birth-to-physical-maturity-there-is-a-rapid-increase-in-function-and-ability-to-cope-with-external-stressors-in-all-dogs-then-as-dogs-age-health-and-function-begin-to-decay-until-death-eventually-occurs-either-directly-from-a-disease-or-more-often-because-humans-are-forced-to-make-the-difficult-choice-to-euthanize-a-dog-because-of-pain-or-poor-quality-of-life-lifespan-is-simply-the-amount-of-time-a-dog-is-alive-healthspan-is-the-period-of-life-where-they-are-living-full-healthy-lives-before-any-major-illness-or-functional-decline">From birth to physical maturity, there is a rapid increase in function and ability to cope with external stressors in all dogs. Then, as dogs age, health and function begin to decay until death eventually occurs, either directly from a disease or, more often, because humans are forced to make the difficult choice to euthanize a dog because of pain or poor quality of life.&nbsp; Lifespan is simply the amount of time a dog is alive. Healthspan is the period of life where they are living full, healthy lives, before any major illness or functional decline.



<p id="the-figure-below-shows-different-possible-trajectories-for-a-dog-s-life-increasing-healthspan-means-giving-dogs-more-time-in-good-health-a-treatment-that-extends-healthspan-can-slow-age-related-decline-in-health-and-increase-this-proportion-of-life-spent-in-good-health-even-if-it-doesn-t-extend-lifespan">The figure below shows different possible trajectories for a dog’s life. Increasing healthspan means giving dogs more time in good health. A treatment that extends healthspan can slow age-related decline in health and increase this proportion of life spent in good health even if it doesn’t extend lifespan!&nbsp;



<figure class="wp-block-image is-resized"><img loading="lazy" decoding="async" src="https://lh3.googleusercontent.com/68eYyrXIDKSaldaOK0yW_tWNHiZwvuDVHgjwZ-SdeBhLSS8AkpHVXvprQVvavaGyGhps9w6PsqHd9LMvFVJcF9rXtV1MKrwN6A4KSC6hZrYnD4l1ft9ZDVi7hrVk1kJ9z58H8S4F" alt="Chart

Description automatically generated" width="1024" height="550"/><figcaption>The impact of increasing healthspan on minimizing the period of poor health preceding death. From McKenzie, BA. Lacroix-Fralish, ML. Chen, F. (2022)The phenotype of aging in the dog: A narrative review. J Amer Vet Med Assoc.</figcaption></figure>



In our view, the goal of maximizing healthspan is equally, if not more important than extending lifespan. Therapies which delay death but do not prolong healthspan might actually reduce overall quality of life by prolonging the period of disability preceding death. Giving dogs and their humans more good quality time together means extending the period of good health, not just the length of life.&nbsp;



Of course, any therapy which extends healthspan will automatically extend lifespan for many dogs because the number one cause of death is euthanasia. If we improve quality of life and function in older dogs, owners will be able to have more joyful time with their canine companions.&nbsp;



Currently, veterinary medicine tends to focus on diagnosing, treating, and sometimes preventing individual disease. However, the most important underlying cause for nearly all diseases in adult dogs is aging. The most effective way to extend the healthy period of life is to target the basic mechanisms of aging that reduce our function and ability to cope with stress and/or fight off disease. Targeting these mechanisms could potentially prevent both heart disease and cancer in many dogs, as well as many other diseases we tend to think of as unrelated.&nbsp;



Healthspan isn’t easy to measure. What is considered “good health” is subjective. The goal of preventing all age-related changes in function and all disease probably isn’t realistic, at least for now. A more practical approach is to consider the number of age-related illnesses that occur, the age at which they happen, and the overall quality of life dogs experience. If we can find treatments that have a clear impact on these measures, we can say we are extending healthspan, and we are likely to also be extending lifespan by improving quality of life and delaying death from illness and euthanasia. As our understanding of aging in dogs improves, and as we develop better tools to measure health and quality of life, we will continue to make progress towards our goals of extending healthspan and giving dogs and their humans more good time together.



<h2 class="has-xl-font-size wp-block-heading" id="loyal-recruited-over-500-dogs-to-participate-in-a-study-assessing-two-tools-for-measuring-frailty-and-health-related-quality-of-life-in-dogs" style="font-style:normal;font-weight:600">Loyal recruited over 500 dogs to participate in a study assessing two tools for measuring frailty and health-related quality of life in dogs.</h2>



<h2 class="has-xl-font-size wp-block-heading" id="read-our-healthspan-study-highlights" style="font-style:normal;font-weight:600">→ <a href="https://blog-admin.loyalfordogs.com/how-scientists-measure-aging-through-healthspan-frailty-and-quality-of-life/">Read our Healthspan study highlights.</a></h2>

Aging impacts dogs in multiple ways, and these impacts reduce both lifespan (the number of years lived) and healthspan (the number of healthy years). Older dogs experience diminished physical health and function, decreased resilience, lower resistance to stress and disease, and undesirable changes in behavior and social functioning. 

Aging also affects the bond between dogs and their human family members, often imposing emotional, financial, and other burdens on caregivers. By targeting the underlying mechanisms of aging, Loyal seeks to mitigate the source rather than just the specific physical or behavioral manifestations of aging.

5 signs of looking old: greying or thinning of hair, loss of muscle, clouding in eyes, limping, or loss of physical function

The most familiar signs of aging are dogs graying, thinning of hair, loss of muscle, and clouding in eyes. Pet parents also frequently notice changes in physical function. Our dogs may be less active or have difficulty going up and down stairs or walking on slippery floors. They may also exhibit a loss of hearing, limping or other signs of discomfort, and a general decline in enthusiasm and energy. 

Most of us can easily tell a dog is an old dog through an intuitive assessment of appearance, movement, and demeanor without being able to detail all the specific features that signal age. One interesting challenge for canine aging science is to be able to break this assessment down into components and identify specific markers of physical aging. This would be especially useful since not all dogs age in the same way or at the same time, so biological age isn’t exactly matched with chronological age. 

We can tell when a dog is “old,” but what we are really seeing is their biological age, not how many years they have lived. A six-year-old Great Dane, for example, may look a lot older than a ten-year-old miniature poodle because giant-breed dogs age physically earlier and faster than small-breed dogs. Having tools to tell us the true biological age of individual dogs would help us understand how and why each dog ages differently. These tools would also help us determine how longevity-promoting therapies affect aging dogs and determine whether these treatments offer meaningful benefits.

Not all physical changes that occur with aging are visible, of course. Changes in the structure and function of internal organs have significant health effects even though they are invisible from the outside. Old dogs may have less energy, less strength, less tolerance for exercise, less resilience in the face of physical stress, such as heat or cold, and less resistance to disease. Chronic health problems, such as arthritis and other inflammatory diseases, kidney disease, heart disease, and many others become more common with aging, and these can seriously degrade well-being and quality of life. 

One of the most common diseases of aging, and one of the leading causes of death in old dogs, is cancer. The details of how cancer develops are complex and vary with different types of cancer. However, age-related damage to DNA and other components of cells, reduction in the function of repair systems, changes in immune system function and the internal environment of the body all make cancer more likely to occur and progress to the point of clinical disease as dogs age. 

One of the exciting aspects of longevity medicine is that by targeting the general aging changes that support cancer development, it may be possible to prevent many different kinds of cancers at once, rather than targeting the specific mechanisms behind each type separately.

6 signs of acting old: increasing in barking, loss of housetraining, reduction of appetite, increasing in fear and confusion, decline in activity, or reduction of social interactions

Changes in behavior are another common and critical effect of aging in dogs. Ultimately, these changes may lead to Cognitive Dysfunction Syndrome (CDS), a phenomenon very similar to dementia and some types of Alzheimer’s disease in humans. This condition disrupts sleeping patterns, social relationships, housetraining and increases fear and confusion, which all seriously undermine quality of life for our dogs and the human-animal bond. These changes often lead to euthanasia even for dogs in otherwise good physical health. Slowing the aging changes in the brain that lead to CDS and other behavior changes would lead to significant improvements to both healthspan and lifespan in dogs.

Dog parents and veterinarians sometimes think of aging-induced changes as natural and inevitable. While this can be comforting when faced with age-related diseases we cannot yet eliminate, we, at Loyal, are focused on the fact that aging is just another manifestation of biology. Scientific investigation can help us to understand the mechanisms of aging and intervene to preserve health and quality of life for our canine companions.

Signs of senior years: looking old, feeling old, and acting old

Aging impacts dogs in multiple ways, and these impacts reduce both lifespan (the number of years lived) and healthspan (the number of healthy years). Older dogs experience diminished physical health and function, decreased resilience, lower resistance to stress and disease, and undesirable changes in behavior and social functioning.&nbsp;



Aging also affects the bond between dogs and their human family members, often imposing emotional, financial, and other burdens on caregivers. By targeting the underlying mechanisms of aging, Loyal seeks to mitigate the source rather than just the specific physical or behavioral manifestations of aging.



<h2 class="wp-block-heading" id="looking-old">Looking Old</h2>



<figure class="wp-block-image size-large"><img loading="lazy" decoding="async" width="1024" height="550" src="http://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869-1024x550.jpg" alt="5 signs of looking old: greying or thinning of hair, loss of muscle, clouding in eyes, limping, or loss of physical function" class="wp-image-370" srcset="https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869-1024x550.jpg 1024w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869-300x161.jpg 300w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869-768x412.jpg 768w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869-1536x824.jpg 1536w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/20220617_post03-e1661442972869.jpg 1770w" sizes="(max-width: 1024px) 100vw, 1024px" /><figcaption>5 signs of looking old: greying or thinning of hair, loss of muscle, clouding in eyes, limping, or loss of physical function</figcaption></figure>



The most familiar signs of aging are dogs graying, thinning of hair, loss of muscle, and clouding in eyes. Pet parents also frequently notice changes in physical function. Our dogs may be less active or have difficulty going up and down stairs or walking on slippery floors. They may also exhibit a loss of hearing, limping or other signs of discomfort, and a general decline in enthusiasm and energy.&nbsp;



Most of us can easily tell a dog is an old dog through an intuitive assessment of appearance, movement, and demeanor without being able to detail all the specific features that signal age. One interesting challenge for canine aging science is to be able to break this assessment down into components and identify specific markers of physical aging. This would be especially useful since not all dogs age in the same way or at the same time, so biological age isn’t exactly matched with chronological age.&nbsp;



We can tell when a dog is “old,” but what we are really seeing is their biological age, not how many years they have lived. A six-year-old Great Dane, for example, may look a lot older than a ten-year-old miniature poodle because giant-breed dogs age physically earlier and faster than small-breed dogs. Having tools to tell us the true biological age of individual dogs would help us understand how and why each dog ages differently. These tools would also help us determine how longevity-promoting therapies affect aging dogs and determine whether these treatments offer meaningful benefits.







<h2 class="wp-block-heading" id="feeling-old">Feeling Old</h2>



Not all physical changes that occur with aging are visible, of course. Changes in the structure and function of internal organs have significant health effects even though they are invisible from the outside. Old dogs may have less energy, less strength, less tolerance for exercise, less resilience in the face of physical stress, such as heat or cold, and less resistance to disease. Chronic health problems, such as arthritis and other inflammatory diseases, kidney disease, heart disease, and many others become more common with aging, and these can seriously degrade well-being and quality of life.&nbsp;



One of the most common diseases of aging, and one of the leading causes of death in old dogs, is cancer. The details of how cancer develops are complex and vary with different types of cancer. However, age-related damage to DNA and other components of cells, reduction in the function of repair systems, changes in immune system function and the internal environment of the body all make cancer more likely to occur and progress to the point of clinical disease as dogs age.&nbsp;



One of the exciting aspects of longevity medicine is that by targeting the general aging changes that support cancer development, it may be possible to prevent many different kinds of cancers at once, rather than targeting the specific mechanisms behind each type separately.







<h2 class="wp-block-heading" id="acting-old">Acting Old</h2>



<figure class="wp-block-image size-large"><img loading="lazy" decoding="async" width="1024" height="611" src="http://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823-1024x611.png" alt="" class="wp-image-387" srcset="https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823-1024x611.png 1024w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823-300x179.png 300w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823-768x458.png 768w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823-1536x916.png 1536w, https://blog-admin.loyalfordogs.com/wp-content/uploads/2022/08/6_signs_of_acting_old_in_dogs-blog-e1661545386823.png 1569w" sizes="(max-width: 1024px) 100vw, 1024px" /><figcaption>6 signs of acting old: increasing in barking, loss of housetraining, reduction of appetite, increasing in fear and confusion, decline in activity, or reduction of social interactions</figcaption></figure>



Changes in behavior are another common and critical effect of aging in dogs. Ultimately, these changes may lead to Cognitive Dysfunction Syndrome (CDS), a phenomenon very similar to dementia and some types of Alzheimer’s disease in humans. This condition disrupts sleeping patterns, social relationships, housetraining and increases fear and confusion, which all seriously undermine quality of life for our dogs and the human-animal bond. These changes often lead to euthanasia even for dogs in otherwise good physical health. Slowing the aging changes in the brain that lead to CDS and other behavior changes would lead to significant improvements to both healthspan and lifespan in dogs.



Dog parents and veterinarians sometimes think of aging-induced changes as natural and inevitable. While this can be comforting when faced with age-related diseases we cannot yet eliminate, we, at Loyal, are focused on the fact that aging is just another manifestation of biology. Scientific investigation can help us to understand the mechanisms of aging and intervene to preserve health and quality of life for our canine companions.

Healthspan: the healthy prime of life

Loyal recruited over 500 dogs to participate in a study assessing two tools for measuring frailty and health-related quality of life in dogs.

→ Read our Healthspan study highlights.